When power is first applied to a chip (or integrated circuit) a reset signal is often asserted to put the chip into a known state to allow proper operation. In conventional systems, a Power-On-Reset (POR) circuit applies a reset signal for a specified amount of time after power has been applied. The reset signal is held long enough to extend longer than the time for the chip to completely receive power.
Conventional approaches often use an analog circuit to assert the reset signal after the power achieves a certain voltage threshold level. The reset signal is held for a specified amount of time. The POR circuit can be implemented externally to the chip with the reset signal being supplied as an input to the chip. In some cases, the POR circuit can be implemented as an analog component on the integrated circuit.
It would be desirable to implement a power-on reset circuit using only digital circuitry.